In message <19980924235128.24801.qmail@gurney.reilly.home>, "Andrew Reilly" wri
tes:
>True, but there are other formats on DVD now, and there will probably
>be others in the future. There can already be Dolby ProLogic in the
>stereo tracks, or DTS (which is six full bandwidth channels, I think), 
>and now MLP (Meridian Lossless Packing) has been admitted, and that
>can manage up to 64 channels (well, I'll believe that when I see more
>of the specs, but I've seen channel allocation lists for up to eight.)
>I believe that MPEG is available on some DVDs, at least in Europe, and 
>we know that software decoders for that are available.

That's a good point.  Given the wide variety of possible formats, it's
important to consider which ones will be used by the majority of
discs, since the most benefit would be gained by supporting those.

>The most likely scenario for the free software community that I can
>think of, though, is either raw PCM or an as-yet unknown free
>compression scheme, onto CD-ROM or DVD-ROM (or hard-disk or internet).

Well, Linear PCM is mandatory for the proposed DVD-Audio standard, so
that would take care of all those discs.  DVD-Video isn't as nice,
since the only requirement is for either PCM or Dolby Digital (for
NTSC discs, anyway), and everything else is optional.  Almost all of
the DVD-Video discs out now have Dolby Digital, and I think that will
continue to be the case.  Even DTS discs will likely include Dolby
Digital (though it might not be 5.1) because there isn't enough space
to do PCM and DTS while keeping the video quality high.

I'm not sure about DVD-ROM-- presumably the ones currently available
use PCM just like their CD-ROM counterparts.

>I think you'll find that many DVD-supporting video cards also have the
>audio decode, but perhaps they do a mix-down to two channels.

Hmm, I'll have to look into that.  I would guess that most, if not all
of them, just have have 2-channel decoders, but it would be cool if
high-end cards supported all six.

>Software decode is certainly possible, but making it happen for NetBSD
>could be difficult (to manage), since Dolby wants a licence fee per DD
>decoder.

Ick.  It sounds like the best way to get DD would have to be hardware,
then.  You could always just go out to an external DD decoder, but
that sort of precludes the use of USB speakers. :)